1. Field of the Invention
The present invention relates to a thin film which is suitable for insulation or protection in a semiconductor device, a mask in the fabrication of a semiconductor device, etc.
2. Description of the Prior Art
A variety of films including silica (SiO.sub.2) films, alumina (Al.sub.2 O.sub.3) films, silicon nitride (Si.sub.3 N.sub.4) films, etc., are used as protective films or insulating films of semiconductor devices, and as oxidation masks or diffusion masks in the fabrication of semiconductor devices, etc.
Especially, a silicon nitride film is extensively employed owing to advantages that it is chemically inert, that it is less prone to oxidation, and that ions of sodium etc., do not readily penetrate it.
However, there is a serious problem that when silicon nitride is directly deposited on the surface of a semiconductor substrate or glass, on an interconnection layer, or the like, a large stress acts on the substrate, the glass, the interconnection layer, or the like, to give rise to such defects as cracks and dislocations in the substrate or the like. The magnitude of the stress acting on the substrate or the like becomes greater as the film of the deposited silicon nitride becomes thicker. By way of example, when a silicon nitride film having a thickness of about 1 .mu.m is deposited on a silicon substrate, the silicon substrate warps and can even break.
In order to prevent such an influence of silicon nitride, there has heretofore been proposed a method in which another film, for example, a silica film or a silicon oxynitride (SiON) film is initially deposited on the substrate or the like, and the silicon nitride film is superposed and deposited thereon.
With this measure, it is possible to prevent the influence of the stress which acts from the silicon nitride film on the substrate or the like. The method, however, renders the fabricating process complicated. Moreover, since two films must be used, errors during the process are an important cause for obstructing the attainment of a minute semiconductor device or the enhancement of the density of integration.